Cezar Floroiu, a director at video game developer Ubisoft,
started the thread because he wanted to hear from hackers and
developers who were "making $1,000+/month on side projects". He
wanted to know what those hacker side projects were, which ones
worked and which ones didn't.

The thread — now a year old — is a fascinating glimpse into the
moonlighting lives of software coders and developers who make
money on hobbies in addition to their regular jobs. They include
people who make software for dog kennel operators, a
self-destructing email service that kills spam, and a web site
that helps people find routing numbers for Bank of America.

"All profitable side projects are profitable because they solve a
real pain so people are willing to pay money to have something
that solves their problem," and thread creator Cezar Floroiu
told Business Insider UK.

Floroiu knows this first hand. After going through the
time-consuming process of recruiting his own team, he
built an online platform to measure candidates' skills
before the interview. It's now tested more than 22,000
candidates, and asked more almost 430,000 questions.

"Believe in what you are building," Floroiu said. He offered two
main pieces of advice: "Be open and communicate and learn from
people using your product" and "listen to them and add those
features that are missing."

Below, we've pulled out some of the best examples of "profitable
side projects" from the thread:

A spam-busting,
self-destructing email service.
10MinuteMail
offers users a temporary email address that deletes itself after
10 minutes for users who don't want to give out their more
permanent email. It was created by user modoc, who
claims the service pulls in between 850,000 and 1 million monthly
unique visitors, with two Google AdSense ads turning a tidy
profit. Like dynofuz's site, this site is based on using a simple
tool to solve a common problem.

Selling "libraries" for app prototyping.
Hacker
News user robinhood sells relatively obscure resources that
can be used by designers to prototype the look of apps and
websites, such as Facebook page layouts, online shopping checkout
designs, and website formatting tools. Robinhood claims to have
created a source of "100% passive income," making $45,000 in 2014
while devoting just 30 hours to the site over the year. It's been
so successful that in 2015, he's quitting his job to run the
website full time. "If I make that much money while doing
practically nothing, I can surely make a ton more by actually
working on it every day for a year."

A healthcare website for scheduling medical visits. Self-scheduling
website inquicker.com was founded by user tikley in 2005 as
nothing more than a "hobby" and a "learning opportunity." But it
transformed from side project to full-time job in 2009 after it
began pulling in $20,000 a year. I n 2013, they hit $5 million in
recurring revenue. "If you're doing something without scale, it
will die when you lose interest," tikley says. "It you're doing
something with scale, perhaps it should grow into a bootstrapped
startup."

An e-book on online payment systems. Side
projects don't need to be websites to be profitable. User
zrail
capitalised on an expertise in online payments to write
an e-book on the subject: A year and a half later, it's surpassed
$42,000 in revenue, requiring only occasional updates to reflect
software developments.

Shutterstock

Software solutions for kennel owners. This example required more
effort, but shows how opportunities can arise in unlikely places.
User
leesalminem spent 2014 building software for dog daycare and
kennel owners, which people "went crazy over" at trade shows.
Despite zero marketing they've snagged almost two dozen customers
paying $100/month. The creators benefited by breaking into a
neglected industry with no new software in the last 10 years.